U.S. Pat. No. 4,401,913, to which European published patent application No. 0066783 corresponds, describes a high pressure discharge lamp having an outer bulb having a dome-shaped cap at one end and a screw-in base at the other. The discharge vessel itself is retained in the longitudinal axis of the lamp. The end of the discharge vessel coupled to the end of the bulb which has the screw thread for a base attached thereto is retained by a rigid terminal wire in the bulb. The end of the discharge tube remote from the base is retained in the bulb by a spring element which is held in position by the bulb itself. To hold the spring element in centered location, the bulb is formed with an inwardly extending closed sleeve portion about which the spring, in form of a spiral spring, is wrapped. The spring is provided to permit acceptance of longitudinal tolerances of the discharge vessel, and, also, to compensate for thermal expansion of the discharge vessel, in operation.
Japanese Utility Model No. 48 24637 describes a spiral holding wire to compensate temperature losses. One end of the spiral holding wire is wrapped about the exhaust tube of the discharge vessel, the other end being secured to a rigid holding wire for the discharge vessel. The holding wire is provided to compensate for thermal expansion of the discharge vessel and, simultaneously, to heat the exhaust tube during operation of the lamp.
It has been found that the holding arrangements for discharge vessels within an outer bulb or envelope surrounding the discharge vessel should be improved to retain centricity of the discharge vessel in operation.